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Biomedical subjects

P Arctander

Publications and source records attributed to P Arctander.

33 records · Page 2Linked to original sources
PubMed1998

Polyphyletic origin of the small-bodied, high-arctic subspecies of tundra reindeer (Rangifer tarandus).

In order to investigate the origin of the three small-bodied, high-arctic subspecies of reindeer, Rangifer tarandus pearyi (the Canadian Archipelago), R. t. eogroenlandicus (East Greenland, extinct since 1900 AD), and R. t. platyrhynchus (Svalbard), samples were collected at nine localities from all six of the currently recognized subspecies of the tundra reindeer. A 203-bp-long fragment of the mitochondrial control region was sequenced from 113 reindeer (Rangifer tarandus). The now extinct subspecies R. t. eogroenlandicus was for the first time included in a molecular study; DNA was extracted from four museum specimens (skins and bones) and successfully sequenced. A polyphyletic origin for the three subspecies of small-bodied, high-arctic reindeer is suggested, with R. t. pearyi and R. t. eogroenlandicus being closely related and probably having evolved in high-arctic North America and R. t. platyrhynchus from Svalbard having evolved from Eurasian large-bodied reindeer. The small-bodied, high-arctic reindeer presumably represent ecotypes that have evolved convergently in similar high-arctic environments.

Animals↗
PubMed1998

Population structure of African buffalo inferred from mtDNA sequences and microsatellite loci: high variation but low differentiation.

The African buffalo (Syncerus caffer) is widespread throughout sub-Saharan Africa and is found in most major vegetation types, wherever permanent sources of water are available, making it physically able to disperse through a wide range of habitats. Despite this, the buffalo has been assumed to be strongly philopatric and to form large aggregations that remain within separate home ranges with little interchange between units, but the level of differentiation within the species is unknown. Genetic differences between populations were assessed using mitochondrial DNA (control region) sequence data and analysis of variation at six microsatellite loci among 11 localities in eastern and southern Africa. High levels of genetic variability were found, suggesting that reported severe population bottlenecks due to outbreak of rinderpest during the last century did not strongly reduce the genetic variability within the species. The high level of genetic variation within the species was found to be evenly distributed among populations and only at the continental level were we able to consistently detect significant differentiation, contrasting with the assumed philopatric behaviour of the buffalo. Results of mtDNA and microsatellite data were found to be congruent, disagreeing with the alleged male-biased dispersal. We propose that the observed pattern of the distribution of genetic variation between buffalo populations at the regional level can be caused by fragmentation of a previous panmictic population due to human activity, and at the continental level, reflects an effect of geographical distance between populations.

Animals↗
PubMed1997

Re: Congruence and phylogenetic reanalysis of perching bird cytochrome b sequences.

In a study of the phylogenetic relationships among perching bird mtDNA sequences, Edwards et al. (1991; Proc. R. Soc. London Ser B. 243: 99-107) sequenced part of the mitochondrial cytochrome b gene from 13 perching birds (Passeriformes) and a woodpecker outgroup. However, recently the validity of part of the sequence of the hermit thrush (Catharus guttatus) in that study has been questioned. To determine the effect of inclusion of this apparently chimeric sequence on the conclusions of the original analysis, we reanalyzed these sequences using a different published hermit thrush sequence. In addition, we applied tests of congruence to examine the possibility that the aberrant phylogenetic behavior of chimeric mtDNA sequences might be detected. The reanalysis confirms the ability of slow evolving first and second codon positions of cytochrome b sequences to resolve deep branches in the avian tree. The fact that the new data set does not reject the DNA hybridization tree of these species probably indicates poor ability of the cytochrome b sequences to discriminate among alternative trees, rather than consistency among data sets. Statistical testing of trees based on individual amplified segments of mtDNA indicates that congruence tests may be one useful way of identifying chimeric mtDNA sequences when they have not been detected in the laboratory or during standard phylogenetic analysis.

Animals↗
PubMed1997

Genetic diversity of the attachment (H) protein gene of current field isolates of canine distemper virus.

To characterize the variability of recent field isolates of canine distemper virus (CDV) from different hosts and geographical areas, we conducted nucleotide sequence analysis of the gene encoding the haemagglutinin (H), the attachment protein of this virus. Pronounced differences between field isolates were revealed in comparison to the Convac and Onderstepoort vaccine strains. The diversity of CDV appeared to exceed that determined for measles virus. Phylogenetic analysis also separated the field isolates of CDV from the vaccine strains and provided evidence for the existence of different contemporary genotypes of CDV. Isolates from a Greenlandic sledge dog and a Siberian seal formed a distinct lineage. The remaining isolates formed a group. This group contained two European isolates from mink and ferret, a single lineage comprising three European dog isolates, and another separate lineage of North American isolates from dog, javelina, raccoon and captive leopards.

Amino Acid Sequence↗
PubMed1996

Simplicity-correlated size growth of the nuclear 28S ribosomal RNA D3 expansion segment in the crustacean order Isopoda.

The expansion segments within the eukaryote nuclear 23S-like ribosomal RNA molecule are now well characterized in many diverse organisms. A different base compositional bias, a higher propensity for size variability, and an increased evolutionary rate distinguish these regions from the universally conserved "core" regions of the molecule. In addition, some expansion segments of higher eukaryotes exhibit significant sequence simplicity which is hypothesized to occur by slippage-mediated mutational processes. We describe the discovery of extreme size variation of the D3 expansion segment in the crustacean order Isopoda. Among 11 species D3 varies in size from 180 to 518 nucleotides but maintains a homologous secondary structure. The D3 size is significantly positively correlated to relative simplicity factor (RSF), indicating that growth is most likely by insertion of simple sequences. D3 size and RSF correlate approximately with a morphology-based phylogeny, and within oniscideans RSF increases as more recent divergences occur. The D3 of Armadillidium vulgare, with an RSF of 1.87, is the highest value recorded for any known expansion segment. Regions of high sequence simplicity in nuclear ribosomal RNA were previously only known from the higher vertebrate lineage. Here we demonstrate that this phenomenon occurs in a more extreme condition within a monophyletic invertebrate lineage. The extreme size changes identified could indicate that expansion segments are an extraneous element in the functioning ribosome.

Animals↗
PubMed1996

Extreme genetic differences among populations of Gazella granti, Grant's gazelle in Kenya.

Mitochondrial DNA (mtDNA) control region sequences from six Kenyan Grant's gazelle (Gazella granti) populations were highly divergent among locations. Neighbouring populations not separated by geographical or vegetational barriers exhibited and nucleotide sequence divergence about 14 per cent. A similar level of divergence separates Grant's gazelles from a closely related species, the Soemmering's gazelle (G. soemmeringii). Nuclear microsatellite repeat number variation at two loci also indicated substantial population genetic differentiation. Despite high levels of sequence divergence populations of Grant's gazelles were more closely related to each other than to Soemmering's and Thompson's gazelles (G. thomsoni) as measured by nucleotide sequence divergence at the mtDNA protein coding cytochrome b gene and the nuclear alpha-lactalbumin gene. This pattern of extensive differentiation is hypothesized to have resulted from recently established contacts between formerly allopatric populations.

Alleles↗
PubMed1996

Evidence from milk casein genes that cetaceans are close relatives of hippopotamid artiodactyls.

The inferred transition from terrestrial hoofed mammal to fully aquatic cetacean has been intensively studied with fossil evidence. However, large sections of this remarkable evolutionary sequence are missing. Phylogenetic analysis of extant taxa may help to fill in some of these gaps. In this report, kappa-casein (exon 4) and beta-casein (exon 7) milk protein genes from cetaceans and other placental mammals were PCR-amplified, sequenced, and aligned to previously published sequences. Phylogenetic analyses of the casein data suggest that hippopotamid artiodactyls are more closely related to cetaceans than to other artiodactyls (even-toed hoofed mammals). An analysis of the nuclear casein sequences combined with published mitochondrial cytochrome b DNA sequences also supports the Cetacea/Hippopotamidae sister group. This affinity implies that some of the aquatic traits of cetaceans were derived in the common ancestor of Cetacea and Hippopotamidae. An extant "missing link" to Cetacea may have been overlooked by science since the description of the semiaquatic Hippopotamus in 1758. Paleontological information is grossly inconsistent with this hypothesis. If the casein phylogeny is accurate, large gaps in the fossil record as well as extensive morphological reversals and convergences must be acknowledged.

Amino Acid Sequence↗
PubMed1995

Comparison of a mitochondrial gene and a corresponding nuclear pseudogene.

Nuclear copies of mitochondrial genes have been reported several times. Presented here is a direct comparison of a fragment of the mitochondrial gene coding for Cytochrome b and its assumed nuclear pseudogene in a phylogenetic context. By studying eight such sets of genes a direct measurement of relative rates of several types of substitutions were made. As expected mitochondrial third position transitions are the fastest accumulating substitutions, here indicated to be at least up to 39 times faster than corresponding positions in the supposed nuclear pseudogene. Translocated mitochondrial genes, evolving much slower than their functional 'counterpart', reflect the ancestral-pre-translocated form of the gene. A warning is given against unwanted inclusion of paralogous sequences in phylogenetic analysis and against the use of versatile primers that can promote such incidents.

Amino Acid Sequence↗
PubMed1994

Andean tapaculos of the genus Scytalopus (Aves, Rhinocryptidae): a study of speciation using DNA sequence data.

Tapaculos of the genus Scytalopus are secretive birds which tunnel like mice through dense understory of humid forest in the Andes, Central America, and south-eastern Brazil. Their agoraphobic habits make Scytalopus species highly sensitive to habitat discontinuities, so they are well suited for analyzing diversification patterns in montane forest biota. This study uses DNA sequence data to test hypotheses about past speciation events. The DNA data support that allopatric and parapatric populations with different songs represent different species. The high degree of phylogenetic resolution obtained by DNA-data permits a better description of geographical patterns of endemism. The data suggests that the commonly observed biogeographic pattern, where related species have long linear distributions along the Andes in different altitudinal zones, arose by divergence in disjunct isolates rather than by parapatric divergence. The approach seems well suited for identifying areas that have a special role for the diversification process. The paper finally discusses how detailed phylogenetic studies can be used to test interpretations of biogeographic patterns of high relevance for pinpointing top priority areas for conservation.

Animals↗
PubMed1991

Mitochondrial resolution of a deep branch in the genealogical tree for perching birds.

Animal mitochondrial DNA (mtDNA) is known to contain information about the genealogical relations among closely related species and is shown here to yield information about distant relations as well. Our results also draw attention to the need for caution in using third positions of codons for tree construction. This is evident from comparative studies of the cytochrome b gene in 13 species representing major groups within the order of perching birds (Passeriformes). Sequences of a 924 base-pair segment of this gene were obtained from each of these species via the polymerase chain reaction and a novel set of versatile primers. With a woodpecker sequence as an outgroup, trees that separate songbirds from other perching birds and resolve the ancient branch leading to songbirds were obtained utilizing the conservative first and second positions of codons. Analysis of positions within codons suggests that, for deep branches, the skewed base composition at the fast-changing third positions can result in phylogenetic disinformation, which conflicts with the information retained in the first and second positions. The mitochondrial tree shows broad concordance with that based on hybridization of nuclear DNA; however, parsimony and maximum likelihood methods suggest a close kinship between thrushes and Australian babblers, in agreement with the traditional morphological classification.

Amino Acid Sequence↗
PubMedDate not supplied

Structure of African elephant populations.

The structure of elephant populations from east and south Africa has been analyzed by Georgiadis et al. (1994) on the basis of restriction site variation of mitochondrial DNA. They used F statistics based on identity by descent in tests for subdivision and reached the conclusion that there was a significant differentiation at the continental level, but that "populations were not significantly subdivided at the regional levels." The data were reanalyzed by Monte-Carlo permutation tests where population subdivision was tested by using F statistics based on partitioning the total haplotype diversity among populations. This resulted in identical conclusions at the continental level, but revealed in addition a significant subdivision at the regional level indicating haplotype frequency differences among the populations.

Africa, Eastern↗